#数字运算
print(3+1)
print(40/2)
print (2**3)


#数字类型
print(type(1))
print(type(int('1')) )

#定义序列
today = '2021-9-13'
print(today[0], today[1], today[-1], today[-2])
print(today[0:2], today[-1:-2])